This invention relates to improvements in hydraulic rock drills of a type in which a hammer piston is hydraulically reciprocable to pound an anvil carrying a drill string, and of a type designed to be automatically fed along a channel as the work progresses.
An advantageous feature of the invention is a sleeve type cycle valve within the piston cylinder which cycles during operation of the tool to control the application and relief of pressure fluid relative to the piston to effect reciprocating action of the latter. A particular advantage of the valve is that it does not close a supply port feeding operating pressurized hydraulic fluid to the piston until at about the moment of completion of the power stroke; and it functions to open the supply port just before the piston has completed its return stroke. This mode of operation enables the piston to have the full force of the operating fluid right up to the time of impact on a power stroke; and to be ready for a power stroke as soon as its return stroke is completed.
Another feature of the invention is a slidable spline coupling between the piston and the anvil which enables pounding of the anvil as the piston reciprocates, and also enables rotation of the piston to be transmitted directly to the anvil, whereby the usual rotation transmitting gear train is eliminated.
A further feature of the invention is a beneficial arrangement of components whereby lubrication and cooling of sliding anvil and piston surfaces is provided by circulating oil of the hydraulic system. This feature promotes greater life of sliding surfaces and seals.
Another feature is an hydraulic shock absorbing thrust bearing arrangement which dampens rebounding actions of the anvil following impact, and has the advantage of returning to the anvil energy that would otherwise be wasted in housing vibrations.
And, a still further feature of the invention is automatic feed mechanism which functions to maintain an optimum amount of anvil travel independently of operator judgement.